Treating of tobacco leaves



United States Patent 3,403,688 TREATING 0F TOBACCO LEAVES Wilhelm Kahane, W. 72nd St., New York, N.Y. 10023, and Magdalena Efros and Norbert Efros, New York, N.Y. (both of 597 Beech St., Haworth, NJ. 07641) No Drawing. Filed Feb. 18, 1966, Ser. No. 528,403 15 Claims. (Cl. 131-140) ABSTRACT OF THE DISCLOSURE In processes for treating tobacco, where the gaseous atmosphere around the leaves is recirculated, the fresh air is deradonized before its admission into the gaseous system of the process, by eliminating from it substantial parts of its radon and of the products of the decay thereof, the active deposit.

In curing processes that use smoke in contact with the tobacco leaves, that elimination is performed also on the combustion air before its admission into thesmoke-generating furnaces.

This invention covers a method for the prevention of tobacco leaves from increasing their natural radioactivity after harvest. It consists in the provision of de-radonizing the fresh air before its admission into the gaseous atmosphere of spaces housing treating operations of the tobacco leaves. This method also covers de-radonization of the air before use in burning the fuel which, in fire-curing and in some flue-curing processes, produces the smoke introduced into said atmospheres.

The alpha-particle emitting natural radioelement polonium-210 has been found in cigarette smoke; and radiation from this source is being considered as a possible significant factor in the genesis of bronchial cancer in cigarette smokers. In the autopsy of lungs obtained from cigarette smokers, 1 formerly cigarette smoker, 2 pipe smokers and 8 nonsmokers, polonium-2l0 was found in higher concentrations (0.002 to 0.023 p.c./g.) in lung parenchyma, peribronchial lymph nodes and bronchial epithelium of persons currently smoking cigarettes than in those of nonsmokers (0.001 to 0.002 p.c./g.); while the parenchymal concentrations in the lungs of the two pipe smokers were similar to those of nonsmokers (0.001 and 0.0015 p.c./g.). These findings are compatible with those of the epidemiological statistics, which have shown a much higher lung cancer risk for cigarette smokers than for nonsmokers, and a lung cancer risk for pipe smokers not above that for nonsmokers. Until today no other hypothesis for the origin of cigarette smokers lung cancer that the above mentioned one was found to be consistent with the epidemiological statistics.

The present invention supplements that which we describe in our application Ser. No. 519,409 filed on January 10, 1966, whereby we proposed a method intended to minimize the increase, after harvest, of the tobacco leaves content in those natural radioisotopes which are susceptible to be transferred into the smoke of cigarettes. In the most used treating processes of tobacco, the leaves are kept in spaces whose gaseous atmosphere has one of its sources in the ambient air atmosphere. The presently most advanced versions of the methods for carrying out the opera tions of the treating of tobacco leaves after harvest, such as: curing, aging, humidity adjustments, additions, fermentation, etc., use recirculation of the greatest part of the same air mass within air-tight shut in spaces housing 3,403,688 Patented Oct. 1, 1968 ice the said operations. The most advanced operating schemes still use streams of fresh air for the needed reconditioning of the atmosphere of those spaces in order to maintain the compositions desired in those operations and for the health of the personnel attending to same.

The improvement ofiered by the present invention con sists in the provision that the above mentioned additions of fresh air be freed of their radon and of the so-called active deposit which consists of the isotopes formed as a result of the radons radioactive decay.

We have stated in our above mentioned previous application that, practically, the only natural radioisotopes, which are liable to pass from tobacco into its smoke, are the following daughters of radon: lead-210, bismuth-210 and polonium-2l0, the former two finally decaying to polonium-ZIO. We also stated that their oxides are volatilized practically at their meltingor sublimation points, whose range of 860-888 C. is exceeded mostly by the tobaccos burning temperatures in cigarettes, but less in those of cigars or pipes; and, thus, said radioisotopes may pass from tobacco into the smoke of cigarettes, but less so in that of cigars or pipes. This view is in agreement both with the theory that polonium210 may be an important factor in the initiation of bronchial carcinoma, and with the findings of the epidemiological statistics on smoking and health whereby cigarette-smokers have a much higher mortality risk through lung cancer than cigaror pipe-smokers. Because of the exposure of the tobacco leaves, during present conventional treating operations, to the contact of huge amounts of atmospheric air contaminated with radon and its daughters, we believe that an important part of the content in the above mentioned three isotopes, as actually existing in tobacco, have entered the tobacco leaves after harvest, following the decay of the atmospheric airs radon. In order to assure that the leaves content in said radioelements will remain practically at the same level as that at the time of harvest, we advocate in this invention that, in all treating operations of the leaves during the time elapsed between harvest and use, the atmosphere around the leaves should be prevented from receiving significant amounts of atmospheric radon and of the products of its decay: the short-lived Po-2l8, Pb214, Bi-2l4 and Po-214, and the longer-lived daughters, i.e. the previously mentioned three isotopes Pb-210, Bi210 and Po-210; these latter elements, as we stated, being liable to pass from the cigarettes tobacco into its smoke.

That object is partially attained in the already mentioned modern schemes for carrying out the treating of tobacco by recirculating practically the same mass of air within air-tight shut in spaces, housing each treating operation, and by admitting only the minimum amounts of fresh atmospheric air as may be required for the reconditioning of the atmosphere of those spaces. But because of the need of keeping those amounts of fresh air extremely low, in order to keep low the contamination with radon and active deposit of the gaseous atmosphere of said spaces, the use of those advanced schemes without the provision of the present invention would lead to only an approximate reconditioning of those atmospheres. Therefore, while a first object of this invention is to provide further means for the prevention of the atmosphere around the leaves from receiving atmospheric radon and products of its decay, another object of the present invention is to provide means for the attainment of a better reconditioning of said atmospheres for the same degree 3 of its daughters from entering the said spaces atmospheres.

These two objects are achieved in the present invention by treating the fresh amounts of air for de-radonization before being admitted into the recirculation airs circuit. By de-radonization we understand an operation whereby air is freed of a substantial part of its total content in gaseous radon and active deposit, the latter be ing a tiny suspension in air of the solids consisting of the isotopes born as a result of radon decay. Because, in our new method, the fresh air admitted into the atmosphere of spaces, housing operations such as curing, ageing, etc., is de-radonized, larger amounts of it are admissible; and still the total amount of radon and if its products of decay introduced will not be higher than when using methods that admit but extremely small amounts of fresh air, not de-radonized.

De-radonization of the fresh air, before its admission into the circuit used to recondition an operational spaces atmosphere, may be done by employing one or a combination of the following methods:

(a) Use of a very spacious anteroom between the fresh atmospheric air entrance and its admittance into the operational spaces atmosphere, the capacity of said anteroom being large enough to shelter that air during several days at least. During its very slow travel through the anteroom, the fresh air loses its gaseous radon by radioactive decay at the rate of one-half of its actual content every next 3.8 days. Thus, a one-week sojourn in the anteroom will result in a drop in radons content to as low as one-fourth of the initial content. By using this method the content in the active deposit of the air increases; and therefore the use of this method should be combined with that of the further described de-activation methods.

(b) Passing the fresh air before its admittance, preferably compressed, through a radon-absorption tower counter-currently to the flow of a liquid and in contact with it, that liquid being a solvent of the gas radon; that solvent flowing in a closed circuit including: a cold section, where said solvent gets in direct contact with the compressed fresh air and where radon is dissolved; and a hot section operating at atmo'sphericor at any other low pressure, where radon is released from that solvent. The increase in temperature combined with the drop in pressure in the hot section, as compared to the conditions prevailing in the cold zone, determine the process efficiency. Although high compression is better, that obtained from a fan can be used as well.

The cheapest solvent is water. The coefficient of solubility of radon in water is 12 times as high as that of air in water. The coefiicient of solubility is defined as the ratio of the concentration of a gas in a liquid solvent to the concentration of that gas in the gaseous atmosphere in direct contact with that solvent. It equals e /v :e /v where v is the volume of the liquid in contact with a volume of gas v while e and 2 are the amounts of radon contained in said volumes. According to Henrys laws, the coefiicient of solubility is a characteristic of the natures of the gas and solvent. It is independent of the gas pressure, for concentrations much below saturation, and decreases with increasing temperatures. Because of its extremely low concentrations in the solvent,'the solubility of radon follows closely Henrys law. Table 1 lists coefficients of solubility of radon in water at temperatures between and 100 C., and Table 2 those of radon in different liquid solvents.

TABLE 1.-SOLUBILITY OE RADON IN WATER Teuaperature, C.:

TABLE 2.OOEFF. OF SOLUBILITY OF RADON IN DIFFERENT SOLVENTS Solvent Water Coefi. at 18 C.

In view of the above listed quite high values of radons coefficients of solubility, and because of the very limited amounts of fresh air needed in reconditioning of the atmosphere of the spaces housing the different treating operations of tobacco leaves, a de-radonizing plant of the described type may be both quite compact and economical to operate in spite of the very low diffusion rate due to the airs extremely low content in radon. Selection of the optimum solvent would result from a compromise between compactness, favored by the more efficient solvents, and the cost of evaporation losses, function of the solvents vapor pressure and of its unit price.

The flow diagram would be much similar to those currently used by the chemical, petroleum and gas industries in the recovery of liquid hydrocarbons from a gas phase. The absorption tower may be packed with bubble-trays; or with plates for the flow of the solvent along them, or with ceramic or metallic objects such as Raschig rings, spheres, etc.; or else, the absorption tower may be a hollow structure through which the solvent rains down as a shower against the ascending current of the air to be treated.

When water is used as the solvent, there is no need for the previously mentioned hot section inasmuch as the used water can be further employed for any urban or industrial duty. In this latter case, water may be used in an open circuit. But even when other solvents than water are used, the hot sectionand thus the release of the dissolved radon--may be suppressed because, due to the very slow diffusion, the solvents content in radon will be much below that of saturation.

(c) By circulating the fresh air in contact with successive beds of a radon-absorbent solid, such as activated charcoal, silica-gel, or other solids highly absorbent of radon. The term activated, when used in this specification in connection with charcoal, has no connection whatsoever with radioactivity. It is the usual designation for the increased adsorption-absorption capability of certain grades of charcoal following a suitable chemical treating. The remarkable absorption power of activated charcoal for radon is used in medical radiology to achieve very high concentrations of radon in a minute fragment of charcoal. The flow diagram would be in many respects similar to those used in charcoal-type plants for the recovery of natural gasoline from petroleum gases with the difference that, in the presently proposed application, the periodical cleaning of the charcoal beds may now be done by means of an acidor other chemical-wash instead of blowing steam. Same as in the case of gasoline recovery, the bed submitted to washing will be the most used one, that which Was first to receive the incoming fresh air. As the time duration of the absorption-washing cycle will be quite long as compared to the radons half-life of only 3.8 days, most of the radon retained in the charcoal or silica-gel pores during the absorption period of the cycle would disappear through radioactive decay, leaving back in the pores the active deposit, consisting mostly of the long-lived Pb- 210 with some Po210. This, together with clogging of those pores by common dust from the air justifies the said periodical washing. After that cleaning, the bed will be placed, by aid of the air-piping manifold, at the end of the series of beds as counted in the direction of the airs flow. Thus a counter-currently flow of the air with regard to the absorbent solid mass will be achieved.

Removal of the active deposit from the fresh air is much more important than that of its gaseous radon because of radons quite short half-life and, therefore, of the relative- 1y much higher amounts of active deposits formed in that air by the radons decay. Thus, de-activation of the fresh air is a first requirement in our invention and must be fulfilled even if no attempt is done to remove the gaseous radon.

By using one of the above described methods (b) or (c) de-radonization, as defined in this specification, is fully achieved inasmuch as both, the gaseous radon and the active deposit are removed from the treated air.

De-activation of the fresh air, i.e. the removal from that air of the radon decays products, may be accomplished by washing the air with a liquid such as water or oil, by spraying that liquid in a shower, or by the impact of wet surfaces with the air as in the oil-type filters for cleaning the suction air in engines, or by any means forcing a liquid into an intimate contact with that air, or by filtering the fresh air through porous media such as ceramic materials, coke, activated charcoal, silica-gel, etc.

De-activation of the fresh air may also be accomplished by using the known method of removing solid suspensions contained in gaseous streams by means of electrical precipitation, as in Cottrell and similar processes where deposition of those solids takes place on electrodes, parts of an electric system placed in said gaseous stream.

Another alternate for de-activation, with or without removal of gaseous radon, is that which combines water washing of the fresh air with electrical deposition upon that water. Said water, beside eventual removal of radon due to its solving power, would accomplish de-activation by a combined mechanical and electrical action. The former is achieved through such means as showers, impacts, centrifugal flows, bubbling trays, etc. which impose, mechanically, a contact between air and water, While the electrical action works through the discharge into that water of the electrical charges of the airs suspension, the active deposit. To this effect, differences in the electrical potential will be created between the fresh air and the water. This may be done in many ways; for example, by connecting to a source of alternating current the structure which houses the flow of water and which is thus in electrical contact with it; or by connecting said structure to one of the poles of a direct current source while ionizing the air, before its entrance into that structure, by means of that direct current flowing into said air through the other pole. A particular arrangement would be that with the water connected electrically to that pole of the source which causes discharge of the negative natural charge of Pb-210 which, being the longest lived isotope of all radon descendants, forms by far the largest part of the fresh airs active deposit.

For those tobacco treating operations that employ fuelsmoke in contact with the leaves, as in fire-curing and in some types of flue-curing, we propose that such operations be performed in air-tight shut in spaces and that the initial mass of air and smoke be recirculated and eventually reconditioned for the approximate maintenance of the desired composition, with admission only of the extremely small amounts of fresh air and smoke as may be required by said reconditioning. This invention requires to de-radonize both the fresh air, directly admitted into said spaces gas circuits, and the air used in the production of the fresh fuel-smoke entering those gas circuits. By doing so, a better reconditioning may be achieved for the same degree of prevention of the ambient airs radon and of its daughters from entering the said spaces atmospheres.

What we claim as new is:

1. The method for minimizing the increase of the content in natural radioelements, daughters of radon, of tobacco leaves following their treating by processes in which the tobacco leaves are kept in spaces whose gaseous atmosphere has one of its sources in the ambient air atmosphere, and in which treating processes that gaseous atmosphere is being recirculated and is receiving additions of fresh gaseous streams for the maintenance of its composition;

said method comprising the below described steps in the following sequential order:

the fresh amounts of ambient atmospheric air, that are employed to form said additions, are passed first through a deradonization plant where their deradonization is performed by eliminating from said air substantial parts of the gas radon and of the products of decay thereof, the active deposit, contained;

the second step being the admittance of that deradonized air into the gaseous system of the treating process used.

2. The method described in claim 1, being applied in processes of curing tobacco leaves which use fuel-smoke in the atmosphere around the leaves, with the understanding that the additions of fresh gaseous streams to that atmosphere, as mentioned in that claim, include the additions of fresh amounts of smoke for the maintenance of the composition of that atmosphere, and thus the deradonization of the fresh air, performed as defined in that claim, is executed on both the fresh air which, in the second step of the method, is admitted as such into the atmosphere around the leaves, as well as on the combustion air which, in that second step of the method, is admitted into the furnaces that generate said additions of fresh amount-s of smoke.

3. The method described in claim 1, wherein elimination of radon is done by radioactive decay achieved by the means of passing the fresh air along a very spacious sheltered anteroom, placed before the entrance into the gaseous system of the treating process, the capacity of said anteroom being as high as the total volume of fresh air consumed during several days.

4. The method described in claim 1, wherein the elimination of radon and of the active deposit is achieved by passing the fresh air in contact with a liquid solvent of radon.

5. The method described in claim 4, wherein the solvent is water.

6. The method described in claim 1, wherein the elimination of radon and of the active deposit is achieved by filtering the fresh air through a bed of an adsorbent material.

7. The method described in claim 6, wherein the adsorbent material is activated charcoal.

8. The method described in claim 6, wherein the adsorbent material is silica gel.

9. The method described in claim 1, wherein the elimination of the active deposit is achieved by impinging the fresh air upon a wet surface.

10. The method described in claim 1, wherein the elimination of the active deposit is achieved by forcing a liquid into intimate contact with the fresh air.

11. The method described in claim 1, wherein the elimination of the active deposit is achieved by passing the fresh air through an electric precipitator with electrodes that are parts of an electric system.

12. The method described in claim 11, wherein one of the electrodes is water.

13. The method described in claim 11, wherein the structure of the precipitator is electrically connected to one of the poles of a direct current source while the current flows into the air and ionizes it through the other pole.

14. The method described in claim 12, wherein the water is electrically connected to that pole of the source which causes discharge of the negative natural electric charge of Pb-210.

15. The method described in claim 1, wherein the elimination of radon and active deposit is achieved by 7 8 submitting the fresh air to the combined'ac'tion of forced OTHER REFERENCES water Washing, centrifugal flow and electrodeposition. Agriculture Engineering July 1952, FOrced Ven R f d tilation Tobacco Curing System, pages 429-430.

8 ereuces lte Tobacco, Compartmental Bulk Curing Facilities for UNITED STATES PATENTS 5 Tobacco Research, pages 34-38, vol. 159, N0. 9, Aug. 3,202,157 8/1965 Touton 131-140 X 1964' 3,233,339 2/1966 Long et al. 131140 X ALDRICH F. MEDBERY, Primary Examiner.

3,327,716 6/1967 Kohan et a1. 131-140 X 

